Intraocular lens

ABSTRACT

Intraocular lens implant ( 10 ) for providing accommodation for near vision includes an optic ( 20 ) centrally disposed in a flexible membrane ( 30 ) and at least one haptic ( 40 ) outwardly extending from the flexible membrane. The flexible membrane is adapted in use to facilitate translatable movement of the optic in response to attempted accommodation by the ocular substrate.

FIELD OF THE INVENTION

The present invention relates to an intraocular lens implant forproviding accommodation for near vision, in particular to an intraocularlens implant that provides for anterior translation of the optic uponcontraction of the ciliary muscles.

BACKGROUND OF THE INVENTION

The human eye has two major refracting elements responsible for focusinglight on the retina The cornea is the anterior refracting surfaceresponsible for the majority of the focusing power of the eye equivalentto approximately 43 diopters whilst the remaining power of approximately19 diopters is from the crystalline lens which is a transparentstructure that focuses light in the human eye.

Emmetropia refers to a state of focus of the human eye where objectsviewed at a distance are in focus on the retina. If axial length of theeye is such that the focal point is in front of the retina therefractive error is known as myopia and if the focal point is beyond theretina the refractive error is termed hypermetropia If the focus of theeye is unequal in different meridians the refractive error is known asastigmatism that can be associated with myopia or hypermetropia.

The power of the cornea is a fixed quantity and the ability to maintainfocus for objects closer than infinity depends on altering the focus ofthe crystalline lens.

The human lens is attached to the wall of the eye by fine filamentaryfibers known as zonules that attach the equatorial region of the lens tothe region of the eye wall surrounded by a circular muscle known as theciliary muscle. In an emmetropic individual, when an object in thedistance is viewed the ciliary muscle is relaxed and the zonules areunder tension. The elastic capsule of the lens is taut and the curvatureof the lens is influenced and slightly flattened by these forces. If theobject of regard is changed to a near object a reflex stimulatescontraction of the ciliary body which relaxes the zonular attachments tothe lens. This allows the elastic capsule of the lens and the malleablelens fibers to assume a more spherical shape and due to the increase inpressure in the posterior segment the lens moves forward. Both factorsincrease the focussing power of the lens by the required amount so thatthe near object of regard remains in focus. This process is referred toas accommodation.

Up to the 4^(th) decade the human crystalline lens is capable ofaltering its focus to maintain clarity of vision for near objects by theprocess of accommodation but this power is gradually lost over the nexttwo decades. This is thought to occur due to several factors includingan increased rigidity of the lens fibers, an increase in the diameter ofthe lens, and possible reduced elasticity of the capsule and zonules.The refractive error describing this inability to achieve near focus isknown as presbyopia and is the reason for the progressive need forreading glasses for individuals from the 5^(th) decade of life.

Spectacles or contact lenses placed in the optical pathway can correctthe focus for clarity of vision in patients with myopia, hypermetropia,or astigmatism. The correction of presbyopia includes separate glassesfor reading, bifocal or multifocal spectacles. Simultaneous near anddistant vision can be achieved by multifocal contact lenses that providesimultaneous foci for near and distance. This method however isassociated with reduced contrast in vision that may be disturbing tomany patients.

More recently it has been found that laser surgery can alter the cornealcurvature to correct refractive errors such as myopia, hypermetropia orastigmatism. Phakic intraocular lenses can be placed in the anteriorchamber of the eye or behind the iris to correct myopia or hyperopia andthe lens can be removed and replaced by an intraocular lens implant forthe purpose of correcting a refractive error.

Surgical procedures have also been proposed to restore accommodation inthe presbyopic age group. These include scleral implants to expand thediameter of the globe to counteract the expansion of the crystallinelens that occurs with age. Radial incisions at the limbus have also beenconsidered for the same purpose. These procedures however have notproved to be sufficiently reliable or predictable. Laser procedures canalter the corneal curvature to produce a multifocal refracting surface.Corneal implants placed in the corneal stroma can also produce a similarbifocal or multifocal refraction. Finally intraocular lenses with adiffractive or refractive surface can be constructed to provide multiplefoci and allow simultaneous focus for distance and near vision. Theselenses can be implanted after surgical removal of the crystalline lensor placed in front of the crystalline lens as a phakic implant.Unfortunately all surgical procedures which depend on simultaneous nearand distance vision are compromised by reduced contrast and are oftenassociated with undesirable effects such as haloes around lights whichmay be disturbing to individual patients. The development of anintraocular lens capable of accommodation similar to the crystallinelens in a young individual is therefore extremely desirable.

Opacification of the lens known as cataract formation is a common causeof poor vision in the elderly and can be corrected surgically. Moderncataract surgery is performed by manual extracapsular cataractextraction or by phacoemulsification. Manual extracapsular cataractextraction involves expressing the hard nucleus of the cataract througha 10 mm to 12 mm incision. Phacoemulsification utilises ultrasonicenergy transmitted by a needle to fragment the nucleus and allowaspiration of the cataract through a 2.5 mm to 3.2 mm incision. A smallincision is desirable in cataract surgery to avoid distortion of thecorneal curvature known as astigmatism. In both operations an opening ismade in the anterior capsule to allow removal of the lens contents. Thecapsular bag remnant, however, is left in situ to provide support for anintraocular lens implant which is inserted following removal of thecataract to replace the focussing power of the natural crystalline lens.It is known to provide an intraocular lens implant to replace thecataractous or clear crystalline lens. The power of the lens can beaccurately selected prior to surgery so that the patient is emmetropici.e. clear focus is achieved for objects in the distance. An intraocularlens implant typically comprises a centre focusing element, known as theoptic and a peripheral support structure known as the haptic. The hapticof an intraocular lens is the outwardly extending supporting elementwhich interacts with the anterior and posterior leaflets of the capsularbag remnant to ensure fixation and stability. The optic and the hapticof the intraocular lens may be manufactured from transparent rigidplastics material such as polymethyl methacrylate or from flexibleplastic materials such as acrylic, silicone or hydrogel polymers.Intraocular lens implants manufactured from flexible materials arepreferable to those made of rigid materials because the lens may befolded to allow insertion through a small incision in the sclera oroutercoat of the eye and is then allowed to unfold to its originaldimensions.

The optic and haptic of the intraocular lens may be manufactured fromthe same material as a single piece unit or the haptic may be attachedto the optic by a variety of mechanisms. There may be one or a pluralityof haptics attached to the optic, although the most common configurationincludes an optic with two outwardly extending diametrically opposedhaptics. The purpose of the haptic is to provide optimal centration ofthe optic as well as a means of fixation of the implant within acapsular bag remnant of the original lens following cataract or lensextraction. It is preferable that the haptics conform to the peripheryof the capsular bag to provide a larger surface area of contact betweenthe intraocular lens implant and the capsular bag and to ensurecentration of the optic.

It is also possible to implant a lens in front of the anterior capsulebehind the iris with the haptics resting in the region between the rootof the iris and ciliary processes, known as the ciliary sulcus. Aspreviously mentioned intraocular lenses may also be inserted in phakiceyes to correct refractive errors, such as myopia or hyperopia. In thesecircumstances the intraocular lens implant may be placed in front of thecrystalline lens behind the iris with the haptic providing support inthe ciliary sulcus. Furthermore, as an alternative site of implantationin phakic eyes, intraocular lenses may be inserted in front of the irisin the anterior chamber with the haptics resting in the angle of theanterior chamber.

In all these instances it is preferable that the haptics conform to theperiphery of the capsular bag or to the ciliary sulcus or the angle ofthe anterior chamber in the phakic eye The prior art discloses severalhaptic designs, including a flange style or loop style, which seek tomaximise the surface areas of contact between the intraocular lensimplant and the capsular bag. The most common design includes two loopstyle haptics attached at diametrically opposed points of an opticwherein terminal ends of the haptics extend arcuately towards theperiphery of the capsular bag.

The fixation and stability of the intraocular lens implant is not solelydependent on the rigidity of the supporting haptics of an intraocularlens, but is also dependent on fusion of leaflets of anterior andposterior capsule in the interval between the optic of the implant andthe terminal of the haptic in contact with the periphery of the capsularbag. It is preferable to maintain as large an interval as possible toprovide maximum opportunity for fusion to occur.

Post-operative shrinkage of the capsular bag is not an unusualoccurrence. The aforementioned interval may be maintained by a rigidhaptic which resists shrinkage of the capsular bag, or by a design forhaptics manufactured from flexible plastics which maintains an intervalbetween the terminal of the haptic and the optic in the even ofshrinkage of the capsular bag. In order that the design shouldaccommodate the various sizes of capsular bag that will be encounteredin different individuals as well as the varying degrees of shrinkagethat would occur during the post-operative phase, it is preferable thatthe haptics should be compressible.

A distinct disadvantage however, of the current haptic designs is thatthe haptic terminal may be flexed at any point between the hapticterminal and the haptic optic junction towards the optic such that theinterval between the haptic terminal and the optic is reduced to theextent where migratory fusion of the leaflets of the anterior andposterior capsule fails to occur. The Author has described(International Publication Number WO00/01323) a haptic design whichmaintains an interval between the terminal haptic and the optic andprovides better conformity of the terminal portion of the haptic withthe periphery of the capsular bag.

Previous descriptions of intraocular lenses capable of an accommodativeeffect include lenses constructed to have an induced increase incurvature of the optic of the lens or a change in position of the lensduring attempted focus for near objects. The latter include lenses witha haptic constructed with a hinge to allow forward translation of theoptic with attempted accommodation. This occurs due to the increase inpressure in the vitreous or liquid in the posterior segment of the globeinduced by contraction of the ciliary body. The accommodative effect ofthis type of intraocular lens however varies widely in individualpatients. The unpredictable results of a intraocular lens with a hingedhaptic are due to the differences in fixation that occur with an implantplaced in the capsular bag after cataract surgery or removal of thenormal crystalline lens by similar techniques. The amount of overlap ofthe anterior capsular bag leaflets over the haptic and edge of the opticis variable as is the extent and area of fusion of the anterior capsularleaflets to the posterior capsule. This variability interferes with theability of the hinged haptic to allow forward movement of the optic inresponse to contraction of the ciliary body in attempted accommodationand is an important factor in the unpredictable accommodative effectthat has been encountered in present day accommodative intraocularimplants.

The present invention attempts to overcome at least in part some of theaforementioned disadvantages.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there isprovided an intraocular lens implant for providing accommodation fornear vision comprising an optic substantially centrally disposed in aflexible membrane and at least one haptic outwardly extending from theflexible membrane to fixate the intraocular lens implant in an opticalsubstrate, wherein the flexible membrane is adapted in use to facilitatetranslatable movement of the optic in response to attemptedaccommodation by the ocular substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a plan view of an intraocular lens implant in accordance withthe present invention;

FIG. 2 is a first side view of the intraocular lens implant shown inFIG. 1 in a first position;

FIG. 3 is a second side view of the intraocular lens implant shown inFIGS. 1 and 2 in a second position; and

FIG. 4 is a side view of an alternative embodiment of the intraocularlens implant in accordance with the present invention; and

FIG. 5 is a side view of a further alternative embodiment of theintraocular lens implant in accordance with the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Referring to the Figures, wherein like numerals and symbols refer tolike parts throughout, there is shown an intraocular lens implant 10,including an optic 20 disposed in a flexible membrane 30, and a pair ofdiametrically disposed haptics 40 outwardly extending from the flexiblemembrane 30.

The optic 20 is a substantially circular convex member and may bemanufactured from a transparent rigid plastics material such aspolymethyl methacrylate, or preferably from a flexible plasticsmaterial, such as acrylic, silicone or suitable hydrogels, which wouldallow the optic 20 to be folded and inserted through a small. incisionin the sclera or outercoat of the eye, whereupon the optic 20 reverts toits original shape once implanted in vivo.

The optic 20 may be equi-convex, asymmetrical bi-convex with its steeperradius placed anteriorally, or plano-convex. Preferably the optic 20 isabout 5.0 mm in diameter.

The optic 20 is substantially centrally disposed in the flexiblemembrane 30 such that the optic 20 is surrounded by an annulus 32 offlexible membrane 30 of about 0.05 mm to 0.5 mm in width depending onthe mechanical properties of the plastics material from which theflexible member 30 formed. The annulus 32 of flexible membrane 30laterally extends from a circumferential periphery 22 of the optic 20.The flexible membrane 30 may also have a concertinaed appearance, asshown in FIG. 5, such that it may be resiliently stretched, therebyfacilitating anterior and posterior translation of the optic 20.Typically, the flexible membrane 30 is also elastic.

When the ocular substrate attempts accommodation, the ciliary musclescontract and the flexible and resilient character of the flexiblemembrane 30 facilitates forward translation of the optic 20 from a firstposterior position as shown in FIG. 2 to a second anterior position asshown in FIG. 3. To a certain extent, the degree of anterior translationof the optic 20 of the present invention will be dependent on the widthof the flexible membrane 30, the elasticity of the flexible membrane 30,or the extent to which the concertinaed flexible membrane 30 can beresiliently stretched in response to pressure exerted by the vitreous orliquid in the posterior segment of the ocular substrate on the flexiblemembrane 30 induced by contraction of the ciliary muscles duringaccommodation.

An outermost peripheral edge 34 of the flexible membrane 30 is providedwith a substantially annular relatively rigid rim 36. In the instancewhere the intraocular lens implant 10 is arranged to be folded andinserted through a small incision, the rim 36 should be sufficientlyflexible and resilient to allow folding thereof and then resumption ofits original shape once implanted in vivo.

It will be understood that a cross-section of the annular rim 36 may becircular, quadrangular as shown in FIGS. 2 and 3, or fluted. Further,with reference to FIG. 4, the cross-section of the rim 36 may beL-shaped with a base portion of the cross-section disposed rearwardly ofan upright portion of the L-shaped rim. Preferably, the outermost edge34 of the flexible membrane 30 is disposed rearwardmost of the rim 36,as posteriorally as possible in order for the optic 20 and membrane 30to remain closely in contact with the capsular bag remnant.

In a preferred embodiment of the intraocular lens implant 10, eachhaptic 40 includes a first portion 42 interconnected to a second portion46 by an elbow-shaped bend 44. An end of the first portion 42 remotefrom the bend member 44 of the haptic 40 is attached to the annular rim36 of the flexible membrane 30 at a haptic-membrane junction 49. Thefirst portion 42 of each haptic 40 extends outwardly from the annularrim 36 in an arcuate manner in a clockwise direction.

The second portion 46 of the haptic 40 extends outwardly from theelbow-shaped bend 44 in an arcuate manner in an anticlockwise direction.In other embodiments of the invention it will be appreciated that,alternatively, the first portion 42 could extend outwardly from theannular rim 36 in an arcuate manner in an anti-clockwise direction andthe second portion 46 could extend outwardly from the elbow-shaped bend44 in an arcuate manner in a clockwise direction. A free end of thesecond portion 46 of the haptic 40 comprises a haptic terminal 45 of thehaptic 40.

The haptics 40 may be manufactured from polymethyl methacrylate, orpreferably from flexible plastic materials such as acrylic, silicone orhydrogels.

Preferably the first portion 42 of the haptics 40 are attached to theannular rim 36 at respective diametrically opposed locations. In otherwords, the haptic-membrane junctions 49 are spaced equiangularly aroundannular rim 36.

In use, the haptics 40 facilitates optimal conformation of therespective haptic terminals 45 with a capsular bag by providing twocounterbalanced points 43, 47 for flexion to occur when the haptics 40are compressed by post-operative shrinkage of the capsular bag. This isachieved by the haptic 40, whose first portion 42 extends outwardly fromthe annular rim 36 of the flexible membrane 30 in an arcuate manner andwhose second portion 46 reverses direction such that the elbow 44 isdisposed on the opposite side of the haptic-membrane junction 49 to theperipheral area of the contact of the haptic terminal 45 with thecapsular bag.

Compression of the second portion 46 of the haptic 40 at a flexion point43 distal to the elbow-shaped bend 44 will tend to incline the hapticterminal 45 of the haptic 40 towards the optic 20 and the flexiblemembrane 30, thereby decreasing the interval between the optic 20 andthe flexible membrane 30 of the implant and the haptic terminal 45 ofthe haptic 40 in contact with the periphery of the capsular bag. Thistendency is counterbalanced in the present invention where compressionof the second portion 46 of the haptic 40 at the flexion point 47proximal to the elbow-shaped bend 44 will tend to decrease the intervalbetween the optic 20 and the flexible membrane 30 of the implant and theelbow-shaped bend 44 of the haptic 40 resulting in an expansion of theperipheral are of the second portion 46 of the haptic, therebyincreasing the interval between the optic 20 and the flexible membrane30 of the implant and the terminal 45 of the haptic 40 in contact withthe periphery of the capsular bag.

It is considered within the scope of the invention if one or a pluralityof haptics 40 are attached to the rim 36 of the flexible membrane 30 andthe terminals 45 of the haptics 40 extend in identical or oppositedirections. It will also be understood that alternative haptics 40,other than those described, are deemed within the scope of the presentinvention.

When the ocular substrate attempts accommodation, the ciliary musclescontract and the flexible and resilient character of the flexibleelastic membrane 30 facilitates forward translation of the optic 20 froma first position as shown in FIG. 2 to a second position as shown inFIG. 3. The flexible membrane 30 facilitates anterior and posteriortranslation of the optic 20 in response to pressure exerted by thevitreous or liquid in the posterior segment of the ocular substrate onthe flexible membrane 30 induced by contraction and relaxation of theciliary muscles during accommodation. The magnitude of the anteriortranslation is determined by either the degree of pressure applied tothe surface area of the capsular bag containing the intraocular lensimplant 10 and/or the size of the surface area to which pressure isapplied.

Typically, in prior art systems, such as the intraocular lens with thehinged haptic as described previously, the entire surface area of thecapsular bag containing the intraocular implant has a diameter of about10.5 mm which affords a surface area of about 86.59 mm². By contrast,the portion of the capsular bag acting on the optic 20 and the flexiblemembrane 30 of the intraocular lens 10 of the present invention is about6 mm in diameter which affords a surface area of about 28.27 mm². Thedifference in size of surface area subjected to the same pressureaccounts for about a three-fold increase in forward translation of theoptic 20 of the present invention, compared to other prior art systems,which enhances its magnification. Increased translation is particularlyadvantageous as it is estimated that a 1 mm of forward translation foran intraocular lens implant is sufficient to provide approximately 2diopters of additional effective power depending on the optic power ofthe optic.

The increase in anterior translation of the optic 20 observed with thepresent invention in comparison with prior art systems is readilyillustrated by the following formulae: Let Volume V₁=a₁x₁ where V₁ isthe volume of vitreous fluid acting on the prior art capsularbag-intraocular lens implant complex; a₁ is the surface area of theprior art capsular bag-intraocular lens implant complex; and x₁ is theanterior translation of the prior art capsular bag-intraocular lensimplant complex.

Let Volume V₂=a₂x₂ where V₂ is the volume of vitreous fluid acting onthe optic 20 and the flexible membrane 30 of the present invention; a₂is the surface area of the optic 20 and the flexible membrane 30 of thepresent invention; and x₂ is the anterior translation of the optic 20and the flexible membrane 30 of the present invention.

Let V₁=V₂ since the volume of vitreous fluid is the same in each case,and a₂<a₁ since the surface area of the optic 20 and the flexiblemembrane 30 of the present invention is less than the surface area ofthe prior art capsular bag-intraocular lens implant complex.

P₁V₁=nRT at any given temperature T, where P₁ is the pressure exerted bythe vitreous fluid on the prior art capsular bag-intraocular lensimplant complex. P₂V₂=nRT at any given temperature T, where P₂ is thepressure exerted by the vitreous fluid on the optic 20 and the flexiblemembrane 30 of the present invention.

Let P₁=P₂

P₁=nRT V₁=nRT a₁x₁

P₂=nRT V₂=nRT a₂x₂

nRT a₁x₁=nRT a₂x₂

If a₂<a₁ then x₂>x₁.

In this particular embodiment, the haptics 40 attached to the membrane30 are encapsulated by the anterior and posterior leaflets of thecapsular bag remnant to ensure fixation and stability, thereby renderingthe haptics 40 substantially rigid and immobile even in response tocontraction and relaxation of the ciliary muscles upon attemptedaccommodation. In contrast to the prior art, particularly theintraocular lens implant reliant on hinged haptics as described byCumming in U.S. Pat. No. 6,494,911, anterior translation of the optic 20of the intraocular implant 10 of the present invention is not reliant onthe mobility of the haptic or its flexibility. Whereas the accommodativeeffect in a prior art lens implant relies on the forward or anteriortranslation of the capsular bag-intraocular lens implant complex,anterior translatory movement is only facilitated for the optic 20 andthe flexible membrane 30, since the peripheral area of the implant 10comprising the haptics 40 is stable. The concept of using a flexiblemembrane 30 to facilitate anterior translation of only the optic 20,leaving the haptics 40 fixed to the ocular substrate appears to beunique in comparison to the prior art.

Modifications and variations as would be apparent to a skilled addresseeare deemed to be within the scope of the present invention.

1. An intraocular lens implant for providing accommodation for nearvision comprising an optic substantially centrally disposed in aflexible membrane and at least one haptic outwardly extending from theflexible membrane to fixate the intraocular lens implant in an opticalsubstrate, wherein the flexible membrane is adapted in use to facilitateanterior and posterior translatable movement of the optic in response toattempted accommodation by the ocular substrate.
 2. The intraocular lensimplant according to claim 1, characterised in that an annulus offlexible membrane laterally extends from a circumferential periphery ofthe optic.
 3. The intraocular lens implant according to claim 1 or claim2, characterised in that the flexible membrane is elastic.
 4. Theintraocular lens implant according to any one of the preceding claims,characterised in that the flexible membrane is resilient.
 5. Theintraocular lens implant according to any one of the preceding claims,characterised in that the flexible membrane is concertinaed.
 6. Theintraocular lens implant according to any one of the preceding claims,characterised in that an outermost peripheral edge of the flexiblemembrane is provided with an annular rim.
 7. The intraocular lensimplant according to claim 6, characterised in that a cross-section ofthe annular rim is circular, quadrangular, fluted, of L-shaped wherein abase portion of the L-shaped cross-section is disposed rearwardly of anupright portion of the L-shaped cross-section.
 8. The intraocular lensimplant according to claim 6 or claim 7, characterised in that anoutermost edge of the flexible membrane is disposed rearwardmost of theannular rim.
 9. The intraocular lens implant according to any one ofclaims 6-8, characterised in that the or each haptic are fixed to andextend from the annular rim of the flexible membrane.
 10. Theintraocular lens implant according to any one of the preceding claims,characterised in that the or each haptic is adapted to be encapsulatedby anterior and posterior leaflets of a capsular bag remnant in theocular substrate to ensure fixation and stability of the or each hapticthereto, thereby rendering the or each haptic substantially rigid andimmobile to translatory movement in response to contraction andrelaxation of ciliary muscles upon attempted accommodation of the ocularsubstrate.